In the letter, Sir Paul makes a lyrical appeal for the release of the 28 Greenpeace International campaigners and two freelance journalists who remain locked up in St Petersburg, facing ludicrous charges of piracy and hooliganism. They were detained nine weeks ago following a peaceful protest again Arctic oil drilling.

My first thought was wow, what unlikely pen pals, but it turns out Sir Paul has previously met with Putin in the Kremlin. Here’s my favourite line from his letter:

“Forty-five years ago I wrote a song about Russia for the White Album, back when it wasn’t fashionable for English people to say nice things about your country. That song had one of my favourite Beatles lines in it: “Been away so long I hardly knew the place, gee it’s good to be back home.” Could you make that come true for the Greenpeace prisoners?”

That is a pretty exciting request, whether you’re a Beatles fan or not.

Vladimir Putin certainly seems to be. In 2003 Sir Paul performed to over 100,000 people including the President, in Red Square in Moscow. So it’s amazing to read Sir Paul McCartney, in his own words, describe the global outcry over the detention of the Arctic 30:

“Vladimir, millions of people in dozens of countries would be hugely grateful if you were to intervene to bring about an end to this affair. I understand of course that the Russian courts and the Russian Presidency are separate. Nevertheless I wonder if you may be able to use whatever influence you have to reunite the detainees with their families?”

It’s been a month since Sir Paul wrote to President Putin. This morning, after releasing the letter on his website Sir Paul tweeted this:

...The Russian Ambassador kindly responded saying that their situation ‘is not properly represented in the world media’...

I can’t wait until our brave friends are free so I can tell them about the day one of the most famous icons of the twentieth century wrote to President Putin calling for them to be allowed home. I’m going to be humming “Back in the U.S.S.R” all day.Read the full letter here.

Elena Polisano is a Polar campaign officer, lives in London, and keeps a bee hive on the roof of the Greenpeace UK office.